Efficient Generation of Conforming Voronoi Polygonal Surface Mesh

A novel construction algorithm is presented to generate a conforming Voronoi mesh for any planar straight line graph (PSLG). It is also extended to tesselate multiple-intersected PSLGs. All the algorithms are guaranteed to converge. Examples are given to illustrate its efficiency.     

Numerical study of an ArH2 gas mixture flowing inside and outside a dc plasma torch

The flow of gas mixtures in a dc plasma torch is studied using the CFD PHOENICS (CFD PHOENICS, Berkeley, CA) code. In the model, the cold gas mixture (300 K), initially constituted of 85 vol% Ar and 15 vol% H, is introduced into a power input zone where it takes energy and is ejected in the surrounding atmosphere at constant pressure (10⁵ Pa). The flow is assumed to be in chemical equilibrium. Equations of mass, momentum, and energy are discretized using a control-volume method. The turbulent flow is modeled by a k-ɛ two-equations model for the turbulent kinetic energy and its dissipation rate. Finally, the algebraic coupling equations set is solved by means of the SIMPLEST algorithm, implemented into the CFD code, using a hybrid interpolation scheme. Results concern the effect of the torch power on the ArH₂ flow. The phenomenon is analyzed through the evolution of velocity and temperature inside and outside the torch. From these calculations, the effect of ambient gas entrainment by the jet is emphasized and a comparison of the level of entrained gas is made with experimental data.     

不同型式流场的PEMFC内部传质分析

对采用不同型式流场的PEMFC进行建模,并用控制容积法对控制方程进行离散,求解得到PEMFC内部各物理量的分布以及综合水拖带系数、质子交换膜平均电导率等。分析了采用交趾型流场和常规流场时PEMFC的内部传质以及阴极性能、电池性能和膜性能,结果认为采用交趾型流场时,PEMFC阴极性能高于采用常规流场的PEMFC阴极性能,但质子交换膜的平均电导率低于采用常规流场时。在没有液态水产生时常规流场PEMFC性能高于交趾型流场PEMFC。     

The numerical modelling of a two-dimensional local exhaust system associated with an inclined jet flow

Previous mathematical models employed by the authors have been further developed in order to consider the effect of an inclined jet on the air flow of a two-dimensional bench-slot Aaberg exhaust system. The air flow in this local exhaust ventilation system is solved using two approaches, namely, (i) a simple potential-flow model and seeking the solution of the resulting Laplace equation by means of a boundary-integral technique, and (ii) a turbulent model using the k- formulation and solving the resulting turbulent Navier-Stokes equations by means of a control-volume method and the SIMPLE algorithm. The effect of the angle that the jet makes with the direction of the surface of the workbench and the momentum ratio on the air flow in the exhaust system are investigated. It is found that, by inclining the jet, the system can become more energy efficient and the region of capture of the contaminant from close to the bench can be increased.     

Conjugate conduction convection and radiation heat transfer through hollow autoclaved aerated concrete blocks

A computational fluid dynamics (CFD) model is developed to study thermal performance of hollow autoclaved aerated concrete (AAC) blocks in wall constructions of buildings under hot summer conditions. The goal is to determine size and distribution of cavities (within building blocks) that reduce heat flow through the walls and thereby lead to energy savings in air conditioning. The model couples conjugate, laminar natural convective flow of a viscous fluid (air) in the cavities with long-wave radiation between the cavity sides. Realistic boundary conditions were employed at the outdoor and indoor surfaces of the block. A state-of-the-art building energy simulation programme was used to determine the outdoor thermal environment that included solar radiation, equivalent temperature of the surroundings, and convective heat transfer coefficient. The CFD problem is put into dimensionless formulation and solved numerically by means of the control-volume approach. The study yielded comprehensive, detailed quantitative estimates of temperature, stream function and heat flux throughout the AAC block domain. The results show a complex dependence of heat flux through the blocks on cavity and block sizes. In general, introducing large cavities in AAC blocks, being a construction material of low thermal conductivity, leads to greater heat transfer than the corresponding solid blocks. Several small cavities in a block may lead to small reductions in heat flux, but the best configuration found is a large cavity with a fine divider mesh in which case heat flux reductions of 50% are achievable.     

Coupled heat transfer modes for calculation of cooling load through hollow concrete building walls

A CFD model was developed to study thermal performance of hollow cement wall constructions of buildings under hot summer conditions. The approach employed couples conjugate, laminar natural convective flow of a viscous fluid in hollow building blocks with long-wave radiation between the cavity sides. Realistic boundary conditions were employed at the outdoor and indoor surfaces of the wall. A state-of-art building energy simulation program, ESP-r, was used to determine the outdoor thermal environment that included solar radiation, equivalent temperature of the surroundings and convective heat transfer coefficient. The CFD problem is put into dimensionless formulation and solved numerically by means of the control-volume approach. The study yielded comprehensive, detailed quantitative estimates of temperature, stream function and heat flux throughout the wall domain. A detailed parametric study showed that using a wider cavity within a building block does not necessarily reduce heat flux through the block. Radiation heat transfer between cavity sides may account for a significant fraction of heat flux through the block and neglecting its effect can lead to errors that could be as large as 46%. The geometry of the hollow blocks was demonstrated to affect the heat flux by as much as 30%.     

二维潮流及泥沙数学模型

本文利用控制体积法对沿水溶平均的二维水流及泥沙微分方程进行了离散，建立了二维潮流泥沙数学模型，并利用连云港附近的潮流及含沙量资料对模型进行了验证计算，验证结果表明，无论是水位、流速、流向，还是含沙量都与实测资料符合良好，由此可以看出，本模型不仅能应用于潮流泥沙计算，而且可以推广到各种平面不恒定流的泥沙冲淤计算中。     

基于控制容积面值的对流扩散差分格式

提出了基于控制容积面值的对流扩散差分格式SCVFV，系统地阐述了SCVFV格式的基本思想，给出了SCVFV插值公式的通用表达式，推导了直角坐标系下完整的SCVFV格式的表达式，从理论上分析SCVFV格式的精度、守恒性及反伪扩散性。采用SCVFV格式和CIMPLE算法对带运动顶盖封闭方腔内的三维层流流场进行了数值计算，得到与实验结果比较一致的计算结果。计算结果表明，SCVFV格式具有较高的精度，是一种值得在工程上推广使用的对流扩散差分格式。     

飞机液压系统热载荷仿真分析

针对某型飞机绿液压系统进行AMESim模型搭建,重点论述了外界环境与液压系统之间的热交换作用.介绍了通过控制体算法搭建液压元件模型的过程,最后建立整个绿系统热模型并进行仿真分析,为后续设计燃油-散热器提供仿真数据参考.     

Convergence of an upwind control-volume mixed finite element method for convection–diffusion problems

Summary We consider a upwind control volume mixed finite element method for convection–diffusion problem on rectangular grids. These methods use the lowest order Raviart–Thomas mixed finite element space as the trial functional space and associate control-volumes, or covolumes, with the vector variable as well as the scalar variable. Chou et al. [6] established a one-half order convergence in discrete L ²-norms. In this paper, we establish a first order convergence for both the vector variable as well as the scalar variable in discrete L ²-norms.